let's talk about battery banks- I reckon the "they aren't worth it" thing is wrong

[TommyO]

5. I think what might be happening is we aren't defining who net metering and/or batteries are "good for", while trying to discuss both.

So who do you think that batteries are "good for"?
Because your initial posts appeared to me to be arguing that batteries are a reasonable choice for a residential user in the US now (Ex. "I reckon the 'They aren't worth it' thing is wrong")

And as should be apparent at this point, batteries aren't worth it in the US. There's a few cases where they are (ex. off-grid cabin) - but those are few and far between.

 

[GoldDigger]

You wouldn't necessarily need to. You could use some batteries and toggle on and off grid as needed.

I was just wondering if this "everyone get the same credit for all PV production" rate regime also regulates going off grid via a transfer switch.

Not that it would be economical, I just looked up the Austin, TX rates and your highest tier is a total cost of $0.1684/kWh. That's cheap compared to California.

Cheers, Wayne

Sunking would have jumped in at this point to tell you that the rates in the Peoples's Republic of Austin are only that high because they are subsidizing RE and spending utility money on other "green" causes.

 

[PVfarmer]

So this software is using a lifespan of 15 years? $12,683 / (21,075 * 15) = $0.0401/kWh

It was 25 years.
Not sure exactly how it gets those LCOEs- I'm sure it's in the software or manual somewhere- there's a LOT of info to sort through.
Stochastic simulations? Um....ok.

Take this with a grain of salt- I know more about transformers than I do about "financial parameters".
I assumed there's no sales tax on PV in Cali for instance, some single things have a small effect, some have a huge effect on LCOE, payback, etc.

Btw, this is with a 5 year loan at 5%- for some reason the LCOE is lower with a loan. This is residential net metered- there are also 4 PPA options to start from.

It is free! Well, technically, our taxes paid for it... Give it a try- you could put in the equipment you have, see how it compares to reality, and....wait for it...
It DOES BATTERIES NOW!!!

SAM makes performance predictions and cost of energy estimates for grid-connected power projects based on installation and operating costs and system design parameters that you specify as inputs to the model. Projects can be either on the customer side of the utility meter, buying and selling electricity at retail rates, or on the utility side of the meter, selling electricity at a price negotiated through a power purchase agreement (PPA).
The first step in creating a SAM file is to choose a technology and financing option for your project. SAM automatically populates input variables with a set of default values for the type of project. It is your responsibility as an analyst to review and modify all of the input data as appropriate for each analysis.
https://sam.nrel.gov/

Changed to 15 years, Sacramento would be:
Metric // Value
Annual energy 21,075 kWh
Capacity factor 18.6%
First year kWhAC/kWDC 1,628 kWh/kW
Performance ratio 0.80
Battery efficiency 0.00%
Levelized COE (nominal) 5.31 ¢/kWh
Levelized COE (real) 4.50 ¢/kWh
Electricity cost without system $780
Electricity cost with system $-463
Net savings with system $1,243
Net present value $5,004
Payback period 6.8 years
Net capital cost $12,683
Equity $0
Debt $12,683

 

[TommyO]

So! If you can do as much of the work yourself as possible...as in drive to a warehouse and get the panels wholesale, etc.

Annual energy 21,075 kWh
First year kWhAC/kWDC 1,628 kWh/kW
Net capital cost $12,683

So what I think are the important items from those figures:
system size: 12.95kW (probably 13kW and a bit of rounding)
1628 / 365 / .8 = 5.5 sun-hours (Sacramento)
price per watt: $.97/W

Under $1/W would IMO be a real challenge to do.
Just panels, inverter, racking, wires and no labor are usually going to be over that.
But it is using a 15 year timeframe for that $0.04/kwh, and you could add in the 30% federal tax credit.
So I believe you could be at $0.04/kwh in Sacramento even with a $1.85/W system.

 

[PVfarmer]

Exact same Sacramento as before, with something like a Tesla battery, costing $450kWh:
Metric Value
Annual energy 21,058 kWh
Capacity factor 18.6%
First year kWhAC/kWDC 1,627 kWh/kW
Performance ratio 0.80
Battery efficiency 97.19%
Levelized COE (nominal) 6.28 ¢/kWh
Levelized COE (real) 5.32 ¢/kWh
Electricity cost without system $780
Electricity cost with system $-462
Net savings with system $1,242
Net present value $3,322
Payback period 8.4 years
Net capital cost $15,847
Equity $0
Debt $15,847

And again with lead/AGMs at $250/kWh:
Metric Value
Annual energy 20,892 kWh
Capacity factor 18.4%
First year kWhAC/kWDC 1,614 kWh/kW
Performance ratio 0.79
Battery efficiency 82.40%
Levelized COE (nominal) 6.07 ¢/kWh
Levelized COE (real) 5.14 ¢/kWh
Electricity cost without system $780
Electricity cost with system $-455
Net savings with system $1,235
Net present value $3,697
Payback period 8.0 years
Net capital cost $14,987
Equity $0
Debt $14,987

 

[PVfarmer]

So what I think are the important items from those figures:
system size: 12.95kW (probably 13kW and a bit of rounding)
1628 / 365 / .8 = 5.5 sun-hours (Sacramento)
price per watt: $.97/W

Under $1/W would IMO be a real challenge to do.
Just panels, inverter, racking, wires and no labor are usually going to be over that.
But it is using a 15 year timeframe for that $0.04/kwh, and you could add in the 30% federal tax credit.
So I believe you could be at $0.04/kwh in Sacramento even with a $1.85/W system.

Yep, it really depends on everything to get under $1/W. You really have to know how many feet of wire, how much the electrician will charge (which depends on # of hours so...?) to be precise with it.
Helioscope + SAM is ideal, because you get the feet of wire and a Google layout (and a CAD file!) from HS and SAM does the financial stuff and the same-ish simulations as HS, but no CAD or Google layout.
Obviously, for those I had to guess the cost for wiring, as I only used SAM.

 

[PVfarmer]

This is what I mean- I missed this slight detail- it was set on the top one, this is changed to the bottom one.


And...this is back at 20 years. Set to "mortgage"- if you set it to "standard loan", 4.02 becomes 4.26.
Details, details....The payback was 8 years on the "upper" setting...because all the credit was not accounted for! I think.
Bear with me, haven't done the net metering option with SAM much...

Metric Value
Annual energy 21,075 kWh
Capacity factor 18.6%
First year kWhAC/kWDC 1,628 kWh/kW
Performance ratio 0.80
Battery efficiency 0.00%
Levelized COE (nominal) 4.92 ¢/kWh
Levelized COE (real) 4.02 ¢/kWh
Electricity cost without system $780
Electricity cost with system $-1,656
Net savings with system $2,435
Net present value $24,104
Payback period 3.1 years
Net capital cost $12,683
Equity $0
Debt $12,683

 

[ggunn]

You wouldn't necessarily need to. You could use some batteries and toggle on and off grid as needed.

Using "some batteries" entails a lot more than that, of course. You can't just add batteries to a grid tied system, and a system optimized for off grid operation looks a lot different from one built for grid tie. You could build a system suited well for one or the other, or one which doesn't do either very well. Or you could build two systems and some sort of switching mechanism that would move the PV modules back and forth between them. Any way you slice it it would not be anywhere near a good economic move.

 

[wwhitney]

You can't just add batteries to a grid tied system, and a system optimized for off grid operation looks a lot different from one built for grid tie. You could build a system suited well for one or the other, or one which doesn't do either very well.

OK, I don't know much about inverters, are you saying the hybrid grid-tie/off-grid inverters are a compromise that don't really do either grid-tie or off-grid very well?

Thanks, Wayne

 

[PVfarmer]

Suppose this is your situation, and you don't have net metering, so whenever you are instantaneously generating more electricity that you are using, you get a POCO refundable credit of, say $0.15/kWh, and whenever you are consuming electricity from the POCO it costs you, say, $0.25/kWh. Now suppose your LCOE for PV is less than $0.15/kWh, and so you want to be a PV farmer and install lots of PV and be a net generator. Should you install batteries?

In this case the answers you have been given still apply, and the answer depends on average cost/kWh of battery storage (I'll call that LCOS for levelized cost of storage). With your excess daytime generation you can either:
(A) sell your excess daytime generation at $0.15/kWh
(B) pay the LCOS to put the energy in batteries and use it to avoid $0.25/kWh in nighttime usage charges

So in this example, if your LCOS is less than $0.10/kWh, it is worthwhile to install batteries. The efficient size of the batteries is determined by your nighttime consumption, they are only economic to the extent you are displacing your nighttime consumption while using a reasonable DOD to keep your LCOS low.

Note that this is still an example of the formula many people have given you, that batteries are economically worthwhile when:
POCO sell < POCO buy - LCOS
Note that the PV LCOE doesn't enter into this.

I literally can't suppose that! Is that a hypothetical situation, or would that happen in Cali?
There is no 15 cent refundable credit here, unless you're talking over 5 MEGAw!
If you wanted to install a- Large-Scale Solar(1,000-5,000 kW DC) system in your backyard...
you'd still get 16.7 cents! That's quite a backyard!
The panels might even run a house under a full moon! :happyyes:
You'd have two services, and if your LCOS is less than POCO price, you'd be sitting pretty.

Not sure where this one is going- say your 15 cents is 25 and your PV output is 2 or 3 times your usage...or equal... of course you would!

(A) sell your excess daytime generation at $0.25/kWh
(B) pay the LCOS to put the energy in batteries and use it to avoid $0.25/kWh in nighttime usage charges

 

[PVfarmer]

OK, I don't know much about inverters, are you saying the hybrid grid-tie/off-grid inverters are a compromise that don't really do either grid-tie or off-grid very well?

I'm not following that either...as far as hybrid inverters, there are only 3 choices here. There are of course more than 3, but the pricey ones are pretty much worth it.
Don't buy the Chinese one, obviously!
http://www.cleanenergyreviews.info/solar-inverter-summary

 

[ggunn]

OK, I don't know much about inverters, are you saying the hybrid grid-tie/off-grid inverters are a compromise that don't really do either grid-tie or off-grid very well?

Thanks, Wayne

Sorry, "well" was not the word I should have used. Substitute "economically" for it in an area where the grid is dependable and relatively inexpensive. A hybrid inverter with sufficient battery power to run your whole house in Austin in the summertime would be hugely more expensive than a simple grid tied system with the same size PV array. There's no way that it would be economically attractive just to get around the Value Of Solar differential in kWh charges and credits. BTW, AFAIK the inverters themselves are not hybrid but are battery inverters. The PV charges the batteries through a charge controller and the inverter runs off the batteries.

I don't know how Austin Energy would require you to configure the interconnection for such a system, or even if they would allow it at all.

 

[PVfarmer]

Ok, if anyone wants to take a stab at this?
This price is of course....inflated. Who knows how much this is:

1

Electrical Design Diagram

Service

9000129

But just throw a number out there if you want. This is $3.40 a kW.
Knock 40% off, that's $2.04 a kW.
You could do it for less- if you call SMA "A" quality and this one maybe A-...you could go B+ or B. But is there any reason to?
You really can't say until you've done a simulation that takes your local climate/weather etc into account, and then done another one with the other equipment....
and then of course the batteries!!

http://www.wholesalesolar.com/18906...backup-system-with-15-astronergy-solar-panels

 

[TommyO]

Ok, if anyone wants to take a stab at this?
This price is of course....inflated.

Not by a lot.
The panels are $1/W, but probably can be found for $.70/W (And I'm sure can be found for >$1/W as well)

The batteries are $4K for 48V, 415Ah AGM.
That's $500 per 6V 400Ah battery - So that looks reasonable.

The inverter is $3600 - A quick search shows that appears to be reasonable for that inverter model as well..

$1500 for racking, cables, breakers, etc I believe is reasonable.

Knock 40% off, that's $2.04 a kW.

Based on what? Wishful thinking?

You could do it for less- if you call SMA "A" quality and this one maybe A-...you could go B+ or B. But is there any reason to?

Well, most people would probably say "screw it - I'm just going with regular grid tie for half the price. Having the batteries isn't worth spending an extra $4k every 5 years"

 

[ggunn]

He said "Knock 40% off, that's $2.04 a kW."
Based on what? Wishful thinking?

Perhaps he is thinking of the Federal Income Tax Credit, but that's 30%, not 40%, and it is going away 12/31/2016.

 

[PVfarmer]

The panels are $1/W, but probably can be found for $.70/W (And I'm sure can be found for >$1/W as well)

The batteries are $4K for 48V, 415Ah AGM.
That's $500 per 6V 400Ah battery - So that looks reasonable.

The inverter is $3600 - A quick search shows that appears to be reasonable for that inverter model as well..

$1500 for racking, cables, breakers, etc I believe is reasonable.
Having the batteries isn't worth spending an extra $4k every 5 years"

70 cents a watt is $2739 instead of $3900.
You can get better batteries than those for $450/400A/6V, so that's $3600. But 8 batteries for 15 panels is too much- 4 would be plenty. So $1800.
Here's a bigger inverter for $800 less.
http://invertersupply.com/index.php...&cPath=0_259&gclid=CK_vk_Pg5cYCFQGVfgodeE0IZg

So that's $4100 less already.

38.5 cents a watt (as in $1500 for racking etc.) is way too much- that site is charging $150 for 100' of 10 AWG!
It really costs more like $200 for 1000'. (Maybe $300 I forget exactly).
Breakers are like $12, combiner is $97.
25 cents a watt for racking would make it $975- that's too much really.
More like $1000 instead of 1500 for the racking etc.

So that's $2.22 a watt...60 cents/watt for panels and you're down to 2.11.
Stay with the 8 batteries and it's 2.50 a watt.
But buying too many batteries is one of the biggest pitfalls- eight 300A batteries for $2800 might be better. It all depends on what you're after with them.

And...the batteries will last for at least 10 years if they're treated right.

 

[wwhitney]

I literally can't suppose that! Is that a hypothetical situation

Hypothetical.

Not sure where this one is going- say your 15 cents is 25 and your PV output is 2 or 3 times your usage...or equal... of course you would!

(A) sell your excess daytime generation at $0.25/kWh
(B) pay the LCOS to put the energy in batteries and use it to avoid $0.25/kWh in nighttime usage charges

Of course you would what? Of course you would choose (A), because you get $0.25/kWh without paying for any batteries. With (B), you pay more (for the batteries) to get the same benefit ($0.25/kWh).

Cheers, Wayne

P.S. While we're on the topic of batteries, I'd love to know when someone will make a relatively inexpensive turn-key AC-coupled battery inverter that talks to Enphase microinverters directly (not just via frequency shifting) to turn down production if it exceeds local demand when operating off grid. Just for backup purposes.

 

[PVfarmer]

Hypothetical.
---
Of course you would what? Of course you would choose (A), because you get $0.25/kWh without paying for any batteries. With (B), you pay more (for the batteries) to get the same benefit ($0.25/kWh).
---
P.S. While we're on the topic of batteries, I'd love to know when someone will make a relatively inexpensive turn-key AC-coupled battery inverter that talks to Enphase microinverters directly (not just via frequency shifting) to turn down production if it exceeds local demand when operating off grid. Just for backup purposes.

Hypothetical in Cali, I guess, but...
whenever you are instantaneously generating more electricity that you are using, you get a POCO refundable credit of, say $0.15/kWh, and whenever you are consuming electricity from the POCO it costs you, say, $0.25/kWh.
Isn't that how ggunn said it works in Texas? Just with 10 and 16 cents not 15/25? BUT instead they charge you for your extra PV output?? Did I read that correctly? That's....kinda brutal. That must make the natural gas people smile...
---
Now suppose your LCOE for PV is less than $0.15/kWh
Do you?
(A) sell your excess daytime generation at $0.15/kWh
(B) pay the LCOS to put the energy in batteries and use it to avoid $0.25/kWh in nighttime usage charges

I'm confused- I meant of course you'd want batteries.
With (A) no batteries, selling for 15 and buying back for 25 doesn't compute well.
So if you got batteries you'd:
Subtract the LCOE of PV (15) from the 25 cents you would pay without PV for what you use. 10 cents- that's how much you're really getting paid, until you exceed usage and are getting all 15 cents. Then eventually you hit payback and you're "getting" all 25 cents (because you have no bill) for the usage replaced, and 15 for extra.

Then for nighttime do the same for LCOE (to put it into batteries)+ LCOS (taking it out) <- subtract that sum from the 25 cents you would be paying. That # is how much you're paying at night, until payback- after that point you are making $ during the day, and not losing any at night. If you were getting paid say 30 cents instead of 15, you might want even MORE batteries, so you could feed into the grid at night!

I think I get the micro inverter question- it seems like this puppy might turn a "dumb" inverter into a smart one? Or be able to talk to the Enphases?
It looks like Enphases do TCP so...?

Page 60-
http://files.sma.de/dl/17975/ClusterController_MODBUS-TB-US-en-15.pdf
1077
Active power limitation P (W)
1078
Active power limitation P (%) of PMAX
1079
Active power limitation P via system control

I saw one for $1200.
http://www.sma-america.com/products/monitoring-control/sma-cluster-controller.html

 

[TommyO]

But 8 batteries for 15 panels is too much- 4 would be plenty.

You'll need to explain why that's the case.

What I've seen says you should size your battery bank 2x-4x larger than (panel-wattage*sun-hours)
(actually it's normally computed the opposite direction - size the battery first, then size the panels, but since it's the battery size you're not believing, we'll compute backwards)

So a 3.8kW system in a 5 sun-hour region should have a 37.5kwh-75kwh battery bank.
That'd be 2x larger than what they already have it pre-packaged with, but you're saying it should be made even smaller?

(And saying "8 batteries for 15 panels is too much" without referencing Ah of the batteries shows you either aren't well versed in this or are not very good at communicating about the topic.)

So that's $4100 less already.

By changing to lower/lesser items.
That's not actually showing that their pricing is "inflated" - just that you would choose a lower/lesser items.

that site is charging $150 for 100' of 10 AWG!
It really costs more like $200 for 1000'. (Maybe $300 I forget exactly).

Ok - that ($150 for 100' of 10AWG PV wire) is a bit inflated.
That I'll agree with you.

And...the batteries will last for at least 10 years if they're treated right.

25% DoD for AGM means ~2000 cycles. (Varies depending on which one you're looking at)
2000/365 = 5.4 years.

 

[TommyO]

\
I'm confused- I meant of course you'd want batteries.
With (A) no batteries, selling for 15 and buying back for 25 doesn't compute well.

If it costs you $.30/kwh for the batteries/equipment to store that energy you'd still buy the batteries?
If it costs you $.10/kwh?
If it costs you $.07/kwh?